Field
Embodiments relate to glass and glass ceramic compositions and in particular, to high strength glass ceramic compositions having a combination of petalite and lithium silicate phases.
Technical Background
Lithium disilicate glass-ceramics in the SiO2—Li2O—K2O—ZnO—P2O5—Al2O3—ZrO2 system have been developed and sold for use as dental crowns, bridges, and overlays. Their microstructures of interlocking tabular crystals provide high mechanical strength and fracture toughness and excellent chemical durability. Compositions in this area were invented at Corning, Inc. and patented by Beall et al. in U.S. Pat. No. 5,219,799 (“the '799 patent”).
In addition, known glass-based materials often exhibit intrinsic brittleness or low resistance to crack propagation. For example, an inherently low fracture toughness (e.g., 0.5-1.0 MPa·m1/2 for oxide glass and glass ceramics) makes oxide glass sensitive to the presence of small defects and flaws. As a comparison point, commercially available single-crystal substrates exhibit a fracture toughness value in the range from about 2.4 to about 4.5 MPa·m1/2. Chemical strengthening by, for example, ion exchange processes can provide some resistance to crack penetration at the surface of a glass or glass ceramic by imposing a compressive stress layer in the glass or glass ceramic to a depth (e.g., 50-100 μm) from the surface; however, the crack penetration resistance may be limited and is no longer effective once a crack propagates through the compressive stress layer into the bulk of the glass or glass ceramic. While the strengthening provides some resistance to crack penetration, the intrinsic property of the material (k1c) is not affected by ion exchange. Improvement of the mechanical properties of glass-based materials, in particular with respect to damage resistance and fracture toughness, is an ongoing focus. Accordingly, there is a need to provide materials with improved damage resistance and fracture toughness.
Lithium-containing aluminosilicate glass-ceramic articles in the β-spodumene family that are ion-exchangeable are known that provide damage resistance and fracture toughness. However, β-spodumene based glass-ceramics are generally opaque, which constrains them from display-related or other applications requiring transparency or translucency. Thus, there is a need for a transparent or translucent glass-ceramic material with fast ion-exchanging capability and high fracture toughness.